Fix reply-context speaker confusion with structured metadata pipeline

Previously, when a user replied to Miku's message via Discord's reply
feature, Miku's quoted words were embedded directly into the user's
message text using the format:
  [Replying to your message: "Miku's words"] User's response

This caused two problems:
1. The LLM had to parse "your message" to determine the quoted text
   was MIKU's words — fragile and frequently misattributed
2. When stored in episodic memory as [User]: ..., Miku's quoted words
   were permanently mislabeled under the user's speaker prefix

Now reply context flows through as structured metadata:
- bot/bot.py captures the replied-to text WITHOUT embedding it in prompt
- cat_client.py passes it as discord_reply_context in the WebSocket payload
- discord_bridge.py injects it as agent_input['reply_context'] — a
  CLEARLY LABELED note: [The user is replying to what you (Miku) said — ...]
- miku_personality.py + evil_miku_personality.py render it via
  {reply_context} placeholder in the prompt suffix, between memory
  context and conversation history

This keeps Miku's words as a separate context note, never mixed into
the user's HumanMessage. Episodic memory only stores the user's actual
words. The fallback path (when Cat is unavailable) also uses a cleaner
format with explicit speaker labels.

cat-plugins/miku_personality/miku_personality.py

@@ -91,6 +91,8 @@ def agent_prompt_suffix(suffix, cat):
 
 {tools_output}
 
+{reply_context}
+
 # Conversation until now:
 (Note: In the conversation below, "Human" = the person you're talking to, "AI" = you, Miku. Pay attention to who said what.)"""